Discuss in detail the usage of public, private, protected, abstract and other keywords in PHP

jacklove
Release: 2023-04-02 12:24:02
Original
1781 people have browsed it

The editor below will share with you an article that discusses in detail the usage of public, private, protected, abstract and other keywords in PHP. It has a good reference value and I hope it will be helpful to everyone. Let’s follow the editor and take a look.

Commonly used keywords in PHP

contains many restrictions on functions and classes in PHP Commonly used keywords usually include abstract, final, interface, public, protected, private, static, etc. Below we will analyze and sort out their usage.

Keywords for variables and methods public, private, protected

public has the greatest authority and can be used by subclasses or supported When called after instantiation,

protected means protected, and access permissions can only be accessed in subclasses and this class.

private means private, only It may be that the keyword static

public; echo $this->protected; echo $this->private; } protected function pro_test(){ var_dump(1); } } $obj = new MyClass(); echo $obj->public; // 这行能被正常执行 //echo $obj->protected; // 这行会产生一个致命错误 //echo $obj->private; // 这行也会产生一个致命错误 $obj->printHello(); // 输出 Public、Protected 和 Private $obj->pro_test();//直接报错 ?>
Copy after login

## variables and methods can be accessed in the current class

The function of static is to enable values or methods to be called in a class without instantiation. At the same time, static-modified variables have the function of storing values. For example, if we do not use static, the result of running is as follows:

"; $var++; } test();// 1 test();// 1 test();// 1 ?>
Copy after login

If we add static to the variable, it will become like this

"; $var++; } test();// 1 test();// 2 test();// 3 ?>
Copy after login

Here You may not be able to realize the benefits of doing this in PHP, so let's first assume that the reader is also familiar with JS. There is no static keyword in JS, so if we want to implement a program that can save the results of each program operation as We need to write a program based on the next operation like this.

var glo=0; function test(){ glo++; document.writeln(glo); } test(); test(); test();
Copy after login

This will leak glo into global variables. If more variables are generated, it will lead to memory leaks (memory leaks refer to Variables occupy too much memory space and will not be released)

Copy after login

So compared to languages that do not define static, it has the advantage of retaining variables. It does not leak memory, and it is not easy to cause global variables to be misused (because the scope is not global)

$age=0; $age++; function test1() { static $age = 100; $age++; echo $age."
"; } function test2() { static $age = 1000; $age++; echo $age."
"; } test1(); // 101 test2(); // 1001
Copy after login

The key to class and method The word final

final can only be used to modify class and function. After using final, it cannot be inherited. For example, the following code will directly report an error

class BaseClass { public $public = 'Public'; function test() { echo "BaseClass::test() called\n"; } final public function moreTesting() { echo "BaseClass::moreTesting() called\n"; } } class ChildClass extends BaseClass { public function moreTesting() { echo "ChildClass::moreTesting() called\n"; } }
Copy after login

Special keywords interface,abstract##The meaning of interface is to standardize the programming style. Imagine if it is implemented If we have an interface, then when we use this interface class, we must implement the methods inside, which plays a role in unified naming.

Class can inherit multiple interfaces. Single inheritance between interfaces is achieved through extends. The relationship between class and interface is established through implements

Sample code:

Copy after login

The function of abstract is actually the same as that of interface, but all methods in interface must be implemented, but in classes modified by abstract, There can be one or more abstract modification methods, so we can understand that interface is a special case of abstract (when all methods are abstract methods, they must be implemented). Abstract has the following characteristics:

1. As long as at least one method in the class uses the abstract keyword, then the class is abstract, and the corresponding keyword must be added

2. Abstract Methods only have the declaration part of the method and no method body.

But in my opinion, abstract has several scenarios like this in actual applications

1. Standardize the naming rules of public parts when multi-person programming (without any explanation, the principle Same as interface)

2. To prevent the parent from being instantiated directly, use the

style code as follows:

loan();//打印出loan ?>
Copy after login

The above article discusses in detail the usage of public, private, protected, abstract and other keywords in PHP. This is all the content shared by the editor. I hope it can give you a reference, and I hope you will support the PHP Chinese website.

Articles you may be interested in:

Explanation on how PHP allows the arrays with the same values to form a new array instance


Detailed explanation of solving the problem of inconsistent PHP string lengths


Command line execution of $argv and $argc configuration methods in php script_php example


The above is the detailed content of Discuss in detail the usage of public, private, protected, abstract and other keywords in PHP. For more information, please follow other related articles on the PHP Chinese website!

Related labels:
source:php.cn
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Latest Downloads
More>
Web Effects
Website Source Code
Website Materials
Front End Template
About us Disclaimer Sitemap
php.cn:Public welfare online PHP training,Help PHP learners grow quickly!